Magnetic amplifier of the balanced push-pull type



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I July 13, 1954 s. L. BRADLEY 2,683,857

MAGNETIC AMPLIFIER OF THE BALANCED PUSH-PULL TYPE Filed March 14, 1951 2 Sheets-Sheet l INVENTOR l/rwhy.

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y 1954 S7 L. BRA DLEY 2,683,857

MAGNETIC AMPLIFIER OF THE BALANCED PUSH-PULL TYPE Filed March 14, l951 2 Sheets-Sheet 2 Mae no 2 I] Fig.|B.

WITNESSES: INVENTOR Schu IerLBmdIe BY y Y TTORNEY Patented July 13, 1954 MAGNETIC AMPLIFIER OF THE BALANCED PUSH-PULL TYPE Schuyler L. Bradley, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 14, 1951, Serial No. 215,548

3 Claims. I

This invention relates to amplifiers, and in particular to magnetic amplifiers oi the balanced push-pull type.

Balanced push-pull been utilized which comprised two branches, each of which branches included one or more magnetic core members. in the known magnetic amplifiers, a main alternating current winding was clisposed on each oi the magnetic core members as well as a control winding, a biasing winding and a feedback winding. The biasing windings were connects-cl to a power supply that was independent of the power supply for the feedback winding. The biasing windings and the control windings were so disposed on each of the magnetic core members that when the current flow through the control windings was in a predetermined direction, the flux produced by the current flow through the biasing and control windings in one branch was additive when the fluxes pro duced by current flow throu h the biasing and. control windings in the other branch were in magnetic opposition. In the branch in which the fluxes produced by the biasing windings and the control windings were in magnetic opposition, which branch is the branch that is being driven down, a transition point was reached where the flux produced by the biasing winding the flux produced by the control winning were equal in magnitude and in magne oppcsition. When this transition point was reached, there was a minimum of output current from the branch of the amplifier that was being driven down. ihe fluxes produced by the biasing wincings the control windings in the other branch were additive, thus the output current from this latter branch continued to rise according to the flow of current through the control windings.

When the transition point was reached in the branch that was being driven down, there apneared the greatest difference in the magnitude of the output current from the two branche However, the fee back windings were so disposed on the magnetic core members and so connected in the amplifier circuit that once this transition point had been passed and. the flux produced by the current flow through the control winding was greater ban the flux produced by the current flow through the biasing winding, the output current from the branch that was being driven down considerably increased. 'l his increase in output current from the branch that was being driven clown once the transition point been passed lessened the difierence in the magnitude of the output currents from the two branches and thus lowered the maximum useful output of the amplifier.

An object of this invention is the provision of a gnetic amplifiers have simplified balanced push-pull magnetic amplifier having a maximum of useful output.

Another object of this invention is the provision of a balanced push-pull magnetic amplifier in which a single winding is utilized as a feeclback winding and as a biasing winding to thus secure a maximum of useful output from the amplifier.

Other objects of this invention will becone apparent from the following description i on taken in conjunction with the accompanying drawings, in which:

Figures 1A and 1B are composite diagrammatic representations of apparatus and. circuits Gill'- boclying the teachings of this invention, and.

Fig. 2 is a graph, the curves of which represent the electrical characteristics of the two nonlinear impedance circuits utilized in the system of Figs. 1A and 1B.

Referring to the drawings and, in particular. to Figures 1A and 1B thereof, there is illustrated a regulating system utilized for inain'tain W output voltage of a generator it sub-stun constant. The regulating system comprises, 1 general, a frequency-co1npensating networ voltage rceirence network it and a magnetic ainplifier is disposed to control the excitation c1 regulating generator it, the output of which is disposed to control the excitation of the gene ator H). In this instance, the generator it coinprises a field winding 23 and arm ture windings 2i? connected to supply load conductors 22, and 25. The field winding 28 is disposed to be energized in accordance with the output of a regulating generator #3, the generator illustrated comprising armature windings a soliexcited field winding 32, and a pair of opposed control windings 3 3 and 35.

In order to provide a m asure of the outp of the generator it, the voltage of -h is to l maintained substantially constant, the frequenccompensator i2 is connected through a pcte ti transformer the primary winclin s or" wnfll are connected across the loacl concluctorand 23. As will be understood, many differ quency compensate-rs may employed, t quency compensator in this instance 00 a series-connected compensating reactor to a capacitor 42, and a bank of capacitors of different size disposed to be selectively connected across the circuit by an adjustable contact meinber 46. Thus, the position of the contact i 45 for selectively connecting one of the capaci: :14 in circuit depends upon the frequency of the enerator it which is to be compensated for. As illustrated, the frequency compensator i2 is connectecl to the secondary winding of the trans former 38 through a voltage divioler =35 for the purpose of adjusting the voltage output whic 3 obtained across the output terminals 50 and 52 of the compensator.

In order to provide a sensitive measuring circuit for measuring the deviations of the voltage across the load conductors 22 and 2d, the voltage reference network I l is connected to the output terminals 50 and 52 of the frequency compensator [2. The voltage reference network It in this instance comprises two non-linear impedance circuits 54 and 56 disposed to supply fullwave dry-type rectifiers 58 and 60, respectively. The non-linear impedance circuit 54 comprises a series-connected capacitor 62 and a saturable reactor 64, whereas, the non-linear impedance circuit 56 comprises a parallel-connected capacitor S6 and a saturable reactor 68. An isolating transformer 10 is disposed in the non-linear circuit 56 to isolate the components thereof and the components of the non-linear circuit 56 from the rectifiers 58 and to prevent circulating currents therein. The electrical characteristics of the non-linear impedance circuits 54 audit will be referred to and described more fully hereinafter.

In order to provide for obtaining a variable output from the voltage reference network 14 in accordance with the deviation of the voltage across conductors 22 and 24 from the predetermined value which is to be maintained substantially constant, the output terminals of the rectifiers 58 and Gil are connected in circuit relation with a resistor 12, different portions or sections of which are disposed to be connected in circuit relation with the respective rectifiers, as by means of a sliding contact member it. Thus, the

portion ll of the resistor 12 connected between the contact member M and one of the output terminals of the rectifier 50 will provide a potential which is a measure of the output of the rectiher 59, and the portion of the resistor 12 connected between the movable contact member l t and one of the output terminals of the rectifier 58 will provide a potential which is a measure of the output of the rectifier 58. In order to provide for adjusting the potential across the section 13 of the resistor '12 so as to obtain a substantially zero net eifective potential across the resistor 12, a movable contact member 16 is provided for movement for controlling the size of the portion is or the resistor 12 in circuit relation with the rectifier 53. By adjusting the position of the contact member 76, a net effective zero potential may be obtained across the resistor 72 for a given voltage across load conductors 22 and 24 which is to be maintained substantially constant.

In order to effectively amplify the output from the voltage reference network 14 so as to obtain sufficient power for controlling the excitation of the regulating generator 13, the magnetic amplifier i is connected in circuit relation between the output terminals and I! of the voltage reference network M and the opposed control field windings 3d and 36 of the regulating generator i8. The magnetic amplifier l6 illustrated comprises four saturable reactors 18, 80, B2 and 8 Each of the saturable reactors is provided with an alternating-current winding 86, 88, 99 and 92, respectively, connected to supply the control field windings 3i and 36. Any suitable source of alternating-current power supply may be utilized although in this instance a potential transformer tit is employed, the potential transformer 94 having its primary winding connected across the load conductors 24 and 26. The transformer 94 is provided with two secondary windings 96 and 98, the secondary winding 96 being disposed to supply the alternating-current windings $5 and 8B of the reactors l8 and 8G, respe"- tively, which alternating-current windings are connected in series circuit relation with each other and are connected to the input terminals of a dry-type rectifier E00. Likewise, the secondary winding 98 of the transformer 9 3 is connected to supply the alternating-current windings 90 and 92 of the reactors 82 and 84, respectively, the alternating-current windings so and 92 being connected in series circuit relation with one another and in circuit relation with the input terminals of a dry-type rectifier 32. As illustrated, the output terminals of the rectifiers lot and H32 are connected to supply the control field windings 3 3 and 3'6, respectively, a resistor I88 being connected intermediate an output terminal oi the rectifier I00 and an output terminal of the rectifier I02 and the midpoint of the resistor me being connected to the control field windings 34 and 36. These later connections, provide a potential drop across sections 33 and m5 of the resistor lot which is a measure of the excitation of the control field windings 3A and 3E. The resistor Hill is provided with movable contact members 10B and M8 for adjusting the potential drop across the sections [03 and H35 of the resistor H34 which are connected in circuit relation with the rectifiers Hill and H12, respectively.

As illustrated, a plurality of direct-current control windings H0, H2, [Hi and H6, are provided on the reactors IS, 86, 82 and 8d, respectively, to control the impedance of the alternating-current windings B5, 88, 9G and 92, respectively. The control windings H8 and H2 are connected in series circuit relation with respect to one another, and the control windings l Hi and HE are also connected in series circuit relation with respect to each other. However, the series circuit-connected windings iii} and H2 are corrnected in parallel relation with the series circuitconnected control windings H t and Hi). This parallel circuit is connected to input terminals HS and 52s, which are in turn connected by conductors in and I24 through movable contact members {25 and [28, respectively, of a manually operated switch I30, which will be referred to hereinafter, and conductors 532 and i3 3, respectively, to the terminals H and 15, respectively, of the resistor 12 whereby the control windings H3, H2, H t and H6 are energized in accordance with the net effective potential across the resistor 12, the direction of current fiow through these windings being dependent upon the polarity of the net efiective potential across the resistor 12.

In addition to the direct-current control windings H0, H2, H6 and H5, each or" the reactors l8, 8%, 82 and. 85 is provided with a biasing direct current control winding i351 38, its and M2, respectively, which windings likewise serve as feedback windings. The biasing windings Hit and H38 are connected in series circuit relation with one another and are connected across section 93 of the resistor [M so as to be energized in accordance with the potential across such section and in accordance with the flow of current from the rectifier H36 through the control field winding 34 of the regulating generator :8. Likewise, the biasing windings I48 and 142 are connected in series circuit relation with one another across section H35 of the resistor 5 so as to be energized in accordance with the potential across such section of the resistor lot and in accordance with the flow of current from the rectifier Hi2 through the control field winding 36 of the regulating generator 12. It is to be noted that the biasing windings I and I39 are so disposed on the reactors l5 and 89, respec tively, that the flux produced by the current flowing through such biasing windings is additive to the flux produced by the current flowing through the direct-current control windings iii! and H2, respectively, when the flux produced by the current flowing through the biasing windings its and is at any instance in opposition to the flux produced by the current flowing through the direct-current control windings IH-i and H8, respectively, of the reactors 82 and S l, respectively. On the other hand, when the fiux produced by the direct-current control windings lit and N2 of the reactors I8 and 89 is in opposition to the flux produced by the biasing windings l and I 38, respectively, then it is to be noted that the flux produced by the current flow through the direct-current control windings H 3 and lie of reactors 82 and 8%, respectively, is additive to the flux produced by the current fiOW the biasing windings I and I42, respectiveiy. The polarity of the potential across the resistor of the voltage reference network I l will determine whether or not the fluxes of the direct-current control windings II!) and II 2 of in opposition to the fiux produced as a result of the energization of the biasing windings I36 and 233, respectively.

Each or" the reactors i8, 80, 82 and 54 is also provided witl'i a damping winding I44, Hi6, ids and i respectively, for controlling the satura tioii of the reactors in accordance with the rate oi. change in the excitation of the generator field fig 2 3. Thus, the flux resulting from the rate I" change of the excitation voltage of the gener tor it will oppose the flux of the directcurrent control winding associated therewith on each of he reactors i3, 80, 82 and 84. For this nose, the damping control windings 54%, I45, l 5% are connected in series circuit relal e uppliecl in accordance with the output of the regulating generator !8, such control wine eing connected to the output of the rogu generator It through a potential transbe appreciated, under certain condit will be desirable to effect a manual reguof the output of the generator Iil instead the automatic regulation, which can be obiied with the regulating system just described. i this purpose, a manual control circuit 554 provided, the switch 530 being disposed for operation to disconnect the output of the voltreierence network it from the amplifier it i to connect the manual control circuit 555 to tire gnetic amplifier. The switch we comprises rality of movable contact members I 25, l i5? and 952, the contact members I it 3 ng disposed in circuit-making posies ablish the automatic regulating system witch Ital is in the position illustrated. contact members I55, :58, Hit and 552 are the circuit-opening position when the coniers and 2-3 are in the circuit-clos ing posnon. For a manual regulation of the generator switch 530 is actuated so as to move the contact members I25 and 28 to a circult-opening position and the contact members through 562 to a circuit-closing position.

Z16 reactors and 88, respectively, is additive or The manual control circuit I 54 comprises a suitable bridge circuit, the input terminals 565 and its of which are disposed to be connected across the output circuit of the regulating generator it when the switch I30 is in the manual control position. As illustrated, the manual control circuit comprises a suitable bridge circuit having four legs, one of the legs comprising a resistor I 68, another leg comprising a pair or" parallel but opposed rectifiers I10 and I12, the other legs being formed of a resistor I14, which has an adjustable contact member I76 disposed for movement intermediate the ends of the resistor i1 5, the movable contact member I it being connected to an output terminal I78 of the bridge circuit, toe other output terminal I at of the bridge circuit being connected intermediate the legs formed by the resistor I68 and the parallelconnected rectifiers H0 and H2. Thus, with the switch l3fi disposed for a manual operation of the system, the contact members I 55 and i connect the output terminals I13 and l of the bridge circuit to the direct-current control windings III), H2, IM and H6 of the reactors F53, dd, 32 and 84, respectively, to control the output of the magnetic amplifier and thereby control the energization of the generator I9. By adjusting the movable contact member Hit, the output potential and the polarity of the manual control bridge I 54 can be readily controlled ma ually.

Before putting the regulating system embodying the teachings of this invention into use, ce'tain adjustments of the apparatus must be made. The movable contact member to of the frequency-compensating circuit I2 shouid be adjusted until it completes an electrical circuit to the proper capacitor 44 in order that proper frequency compensation may be obtained. When the proper frequency compensation is obtained, the voltage input to the voltage reference network 12 will be substantially unaffected by changes in frequency of the alternating-current generator I 63.

The slidable contact members it and it of the voltage reference network I4 are adjusted so that there is no voltage at the output of the voltage reference network I 4 when the output voltage from the alternating-current generator #9 is at its regulated value. As regard the magnetic amplifier $6, the slidable contact members and 198 are adjusted until the flux produced the direct current flow through the field wind.- ings 34 and 36 of the generator I e is in oppositic and equal in magnitude when the output volt from the alternating-current generator 45 is its regulated value.

The voltage divider 43 should then be until the voltage input to the voltage refereinetwork !4 is of such a magnitude that the pro=v correction voltage can be applied to the fie d winding 28 of the alternating-current generator It to thus maintain the output voltage 0 alternating-current generator It at its value.

In operation, with the switch 93 posit shown in Fig. 1A of the drawings, in w movable contact members I25 and i253 are in circuit closing position and the movable co members I56 through I 52 are in the circuit interrupting position, if there is an increase or decrease in the magnitude of the voltage output of the alternating-current generator 8!; from its: regulated value, a measure of this increase or decrease in voltage will appear across the output terminals 50 and 52 of the frequency-compensating circuit l2 and thus across the input to the voltage reference network Hi. As hereinbefore mentioned, the frequency-compensating circuit i2 maintaining the input voltage to the voltage reference network It is unaiiected by the frequency of the alternating-current generator iii.

Referring to Fig. 2 of the drawings, there is illustrated a graph, the curves of which represent the electrical characteristics of the non-linear impedance circuits 5d and 56 utilized in the systern shown in Figs, 1A and 1B. Curve 82 represents the magnitude of the current flow through the capacitor 56 and the saturating reactor Ell for various magnitudes of voltages that are im pressed across the input terminals 5% and 52 to the voltage reference network as. Curve 8e represents the magnitude or" the current flow through the capacitor 62 and the saturating reactor 64 for various voltages that are impressed across the input terminals 5! and 52 to the volt" age reference network i 4%. When the voltage irnpressed across the input terminals 533 and 52 to the voltage reference network ld'has a magnitude equal to that represented by H38 on the graph, the current flow through the two non-linear pedance circuits 5% and :36 will be of equal magnitude. When the current flow through these two non-linear impedance circuits is of equal magnitude, the output voltage of the alternatingcurrent generator Hi should be at its regulated value.

As can be seen from Fig. 2 of the drawings, with an increase in the output voltage of the alternating-current generator it (as represented by 18% on the graph), there will be a wide difference in the magnitude of the current that is flowing through the impedance circuit til comprising the capacitor 52 and the saturating reactor and the impedance circuit 56 comprising the capacitor 65 and the saturating reactor 58. The current flow through the impedance circuit 5% is of a smaller magnitude than the magnitude of the current flow through the impedance circuit E l when the output voltage of the alternating-current generator it is above its regulated value. A current of smaller magnitude will fiow through the portion ll of the resistor l2 that is connected to one or" the output terminals of the rectifier fit and the slidable contact member it than will fiow through the portion '53 of the resistor 12 that is connected to one of the output terminals of the rectifiers 58 and the slidable contact member id. The current fiows in opposite directions through the portions H and T3 of the resistor 32 and when the magnitude of the current fiowing in these two portions of the resistor '52 is not equal, there will be a voltage across the resistor F2. The polarity of this voltage and thus the direction of ilow of the current that passes through the resistor 22 to the magnetic amplifier it will be determined by which portion of the resistor l2 has the greater magnitude of current fiowing theretnrough.

If the output voltage of the alternating-current generator it rises above its regulated value, the polarity of the net efiective voltage across the resistor IE will be such that the current to amplifier it will flow through the resistor l2 in the direction of the output terminal ll of the rectifier til, through the conductor i32, the 1novable contact member H5, the conductor 2-2, the input terminal i it of the amplifier it, the parallel circuit comprising the series connected control windings Nil-H2 and H t-HE, the input terminal $28, the conductor i241, movable contact inimember I28, and conductor !34, to output terminal '15 of the voltage reference network Hi. The current flow through the biasing windings H36 and I38 will be in such a direction that the flux produced thereby will be additive to the flux produced by the control windings I It and i 52 respectively. However, the fiux produced by the direct-current flow through the biasing windings it!) and I42 will be in opposition to that flux produced by the direct-current flow through the control windings lit and H6 respectively. When the flux produced by the current flow through the control winding lid is equal in magnitude and opposite to that flux produced by the direct-current flow through the biasing winding led] and the flux produced by the direct-current flow through the control winding 1 it is equal in magnitude and opposite to the fiux produced by the direct-current flow through the biasing winding i 22, there will be a minimum of saturation of the magnetic core members 82 and 8d, the alternating-current windings 93 and 92 then oiiering a maximum of impedance to the current fiow, and thus rendering a minimum of current iiow to the field winding 36. When the flux produced by the current flow through the control windings H 1 and i It rises to a magnitude that is greater than the magnitude of the fiux produced by the current fiow through the biasing windings 48 and 5&2 respectively, there will momentarily be a current how of greater magnitude through the alternating-current windings Eli and 92 than is the case when the fiux produced by the current flow through the control winding I it and the biasing winding Hill is equal in magnitude. When the current fiow through the alternating-current windings 9i! and Q2 increases momentarily the output current from the rectifier H32 and hence the current flow through the biasing windings ltd and M2 increases. This increased current flow in the biasing windings lit and its produces an additional biasing flux to ofiset and oppose the flux produced by the additional current flow through the control windings lit and H6 after the transition point is passed where the magnitude of the fiux produced by the current flow through the control winding i i4 is equal in magnitude and in opposition to that flux produced by the current flow through the biasing winding Hi5. Therefore, the current flow through the field winding 35 remains substantially at the same minimum value first reached even though the flux produced by the current flow through the control windings H4 and lit increases in magnitude beyond that value at which the flux produced by the control windings H4 and HE was first equal in magnitude to the fiux produced by the current fiow through the biasing windings I69 and M2, respectively.

Still assuming the output voltage of the generator it is above its regulated value, with e ch increase in current fiow through the control windings i it and I 12, there is a proportional increase in the total flux produced by the current flow through the control windings H6 and H2. This increased current how in the control windings i ii] and H2 further increases the saturation or" the magnetic core members is and 8t, respectively, thus lowering the impedance of the alternatingcurrent windings 8t and 38, thus increasing the output current of the rectifier it to the biasing windings I36 and 38. The increased current flow through the biasing windings E36 and 538 increase the flux produced by these windings.

Since the fluxes produced by the control windings H and H2 are additive to the fluxes produced by the biasing windings I36 and I38 respectively, the impedance of the alternating-current windings 85 and 88 is further lowered and the current flow through the field winding 34 of the control generator I3 continues to increase in proportion to the current flow through the control windings III] and H2. Thus the feedback to the biasing windings 93%, I38, I40 and I42 which likewise act as feedback windings, is such as to produce a wide diiference in the magnitude of the current flow through the field windings 3'3 and 36 of the generaitor I8 when the output of .ie generator it is not at its regulated value and therefore a maximum of useful output from the magnetic amplifier I6.

The combined flux produced by the directcur rent fiow through the field windings 34 and 36 of the control generator it when the output voltage from the alternating-current generator It is above its regulated value causes the output voltage from the control generator IE to decrease, thus decreasing the voltage across the field winding 28, lowering the output voltage of the alternating-current generator It to its regulated value.

The rapid rise in the flux produced by the current flow through the control windings Ht, H2, III; and H6 is opposed by the flux produccl by the current flow through the damping windings I 44, I45, M3 and I50, respectively. This prevents an overcorrection of the output voltage of the alternating-current generator in and renders a more stable regulating system.

If, however, the output voltage of the aiternating-current generator I0 falls below the regulated value, a measure of the decreased voltage will be impressed across the input terminals 53 and 52 to the voltage reference network It. Referring to Fig. 2 of the drawings, it can be seen that when the output voltage of the alternating-current generator I8 is below the regulated value as represented by I93, the current flow through the non-linear impedance circuit 54 will be of a smaller magnitude than the magnitude of the current flowing through the non-linear impedance circuit 56. When this operating condition exists, the current will flow through the resistor 72 of the voltage reference network is in a direction towards the output terminal i5, through the conductor I3 5, the movable contact member I 23, the conductor I24, the input terminal I28 of the amplifier IS, the parallel circuit comprising the series connected control windings I I 6II2 and IM-I I6, the input terminal H3 of the amplifier I5, the conductor I22, the movable contact member I25, and the conductor IM tothe output terminal H? of the voltage reference network I4. The current flow through the control windings H0, H2, H 1 and HE is in such a direction that the fiux produced by the current flow through the control windings H9 and I! 2 will be opposed to the flux produced by the direct-current flow through the biasing windings I 35 and 38, respectively. The current flow through the control windings H4 and H6 will be in such a direction that the flux produced thereby will be additive to that flux produced by the direct current flowing through the biasing windings I48 and I42, respectively. When the current fiows in this manner through these windings of the magnetic amplifier I6, there will be an increase in the current flow through the field Winding 35 over that value that exists when the output voltage of the alternating-current generator I6 is at its regulated value.

When the output voltage of the alternatingcurrent generator is below its regulated value, the flux produced by the current flow through the control windings H0 and H2 will be in. opposition to the flux produced by the curr nt flow through the biasing windings 35 and I38, respectively, and the current flowing through the field winding at will be decreased and maintained at a minimum magnitude for reasons as hereinbefore mentioned. The combined flux produced by the current flow through the control field windings 34 and 36 causes the output voltage of the control generator I8 to increase to such a value that the output voltage of the alternatingcurrent generator I ii is raised to its regulated value.

As hereinbefore mentioned, the output voltage of the alternating-current generator I0 may be manually controlled by means of the manual control. I54. To switch to manual control, the switch i is first actuated so as to move the contact members I26 and I28 to the circuit interrupting position and the movable contact members I56, I58, 569 and IE2 to the circuitclosing position. With these latter contact members so positioned, the slidable contact member iii; may be actuated towards one end or the other of the resistor I I4. This effects an unbalance of the manual control circuit I54 or Wheatstone bridge in one direction or the other to either increase or decrease the output voltage of the alternating-current generator If].

The amplifier embodying the teachings of this invention has several advantages. Among these advantages is the fact that a single winding on each of the magnetic core structures serves as both a biasing winding and a feedback winding.

As hereinbefore mentioned, the feedback that was obtained heretofore in magnetic amplifiers of the balanced push-pull type acted as a hinrance rather than an aid to obtaining a maximum useful output from the amplifier once the output current of the branch that was being driven down had reached its minimum value and the input current to the amplifier control windings continued to increase in magnitude. However, the feedback obtainable by the amplifier embodying the teachings of this invention aids in obtaining a greater maximum useful output after the output current from the branch that is being driven down has reached its minimum value and the input current to the amplifier control windings continues to increase in magnitude.

Since a single winding on each of the magnetic core structures serves as both a biasing winding and a feedback winding, the initial cost of manufacturing such a magnetic amplifier of the balanced push-pull type is considerably less. Also, since the efiiciency of the amplifier embodying the teachings of this invention is much higher than the emciency of other known types of magnetic amplifiers of the balanced push-pull type, the physical size of the amplifier will be smaller and at the same time it will have a useful output equal to those amplifiers of larger physical dimensions. Such a reduced size can be an important factor when there are space limitations.

I claim as my invention:

1. In a magnetic amplifier of the balanced push-pull type responsive to a variable electrical quantity to effect a control operation, the combination comprising, two pairs of magnetic core members, a load winding disposed on each of the magnetic core members, two rectifiers of the dry type for rectifying the output of the amplifier, the rectifiers having input and output terminals, the load windings on one pair of magnetic core members being connected to the input terminals of one of the rectifiers, the load windings on the other pair of magnetic core members being connected to the input terminals of the other rectifier, a control winding disposed on each of the magnetic core members, the control windings bein responsive to the variable electrical quantity, a biasing-feedback winding disposed on each of the magnetic core members, the biasingfeed back windings on said one pair of magnetic core members being responsive to the output of only said one of the rectifiers, the biasing-feedback windings disposed on said other pair or" magnetic core members being responsive to the output of only said other rectifier, a resistance member connected between an output terminal of one of the rectifiers and an output terminal of the other rectifier, the biasing-feedback windings on said one pair of magnetic core members being connected between one end of the resistance memher and an intermediate point thereof, the biasing-feedback windings on said other pair of magnetic core members being connected between said intermediate point of the resistance member and its other end, the biasing-feedback windings on said one pair of magnetic core members being so disposed that when the flu); produced by the current fiow through the biasing-feedback windings disposed on said one pair of mag netic core members is in magnetic opposition to the flux produced by the current flow through the control windings on the same pair of magnetic core members the flux produced by the current flow through the biasing-feedback windings disposed on said other pair of magnetic core members will be additive to the flux produced by the current flow through their associated control windings.

2. In a magnetic amplifier of the balanced push-pull type responsive to a variable electrical quantity to effect a control operation, the com bination comprising, two pairs of magnetic core members, a load winding disposed on each of the magnetic core members, two rectifiers of the dry type for rectifying the output of the amplifier, the rectifiers having input and output terminals,

the load windings on one pair of magnetic core 7 members being connected to the input terminals of one of the rectifiers, the load windings on the other pair of magnetic core members being connected to the input terminals of the other rectifier, a control winding disposed on each of the magnetic core members, the control windings being responsive to the variable electrical quantity, a biasing-feedback winding disposed on each of the magnetic core members, the biasingfeedbacl; windings on said one pair of magnetic core members being responsive to the output of only said one of the rectifiers, the biasingfeedback windings disposed on said other pair of magnetic core members being responsive to the output of only said other rectifier, a resistance member connected between an output terminal of one of the rectifiers and an output terminal of the other rectifier, the biasing-feedback windings on said one pair of magnetic core members being connected between one end of the resistance member and an intermediate point thereof, the biasing-feedback windings on said other pair of magnetic core members being connected between said intermediate point of the resistance l2 member and its other end, the biasing-feedback windings on said one pair of magnetic core members being so disposed that when the flux produced by the current flow through the biasing feedback windings disposed on said one pair of magnetic core members is in magnetic opposition to the flux produced by the current flow through the control windings on the same pair of magnetic core members the flux produced by the current flow through the biasing-feedback windings disposed on said other pair of magnetic core members will be additive to the fiux produced by the current flow through their associated control windings, and adjustable means connected to the resistance member and disposed to adjust the magnitude of its resistance on either side of said intermediate point to thereby afiect the magnitude of the current flow through the biasing-feedback windings of the magnetic amplifier.

3. In a magnetic amplifier of the balanced push-pull type responsive to a variable electrical quantity to efiect a control operation, the combination comprising, two pairs of magnetic core members, a load winding disposed on each of the magnetic core members, rectifiers for rectifying the output of the amplifier, the rectifiers having input and output terminals, the load windings of one pair of magnetic core members being connected to the input terminals of one of the rectifiers, the load windings on the other pair of magnetic core members being connected to the input terminals of the other rectifier, a control winding disposed on each of the magnetic core members, the control windings being responsive to the variable electrical quantity, a biasing-feedback winding disposed on each of the magnetic core members, the biasing-feedback windings on said one pair of magnetic core members being responsive to the output of only said one of the rectifiers, the biasing-feedback windings disposed on said other pair or" magnetic core members being responsive to only the output of said other rectifier, the biasing-feedback windings on said one pair of magnetic core members being so disposed that when the flux produced by the current flow through the biasingfeedback windings disposed on said one pair of magnetic core members is in magnetic opposition to the fiux produced by the current flow through the control windings on the same pair of ma netic core members, the flux produced by the current flow through the biasing-feedback windings disposed on said other pair of magnetic core members will be additive to the flux produced by the current flow through the associated control windings, and a damping winding disposed on each of the magnetic core members in predetermined relation to the associated con trol winding, the damping winding on each magnetic core member being capable of producing a flux in opposition to the 11m: produced by the associated control winding.

References Cited in the file or" this patent UNITED STATES PATENTS Number Name Date 1,914,220 Sorensen et a1 June 13, 1933 2,306,998 Claesson Dec. 29, 19%2 2,464,639 Fitzgerald Mar. 15, 1951 2,552,952 Gochet et a1 May 15,1951

OTHER REFERENCES Publication, A. I. E, Magnetic Amplifiers, by W. Geyger, 1949. Misc. paper 50-93. 

